It is desirable in a wide variety of applications to provide paints which contain biocidal agents. For example, as recognized by the present invention, it would be advantageous to provide a biocidal agent in paint which is used to cover bathroom walls, to inhibit the development of fungus on the walls. As another example, and of particular concern to the present invention, is the provision of biocidal paint (often referred to as "antifouling coatings") for ships' hulls.
Tributyltin (often referred to as organotin) biocidal compounds were added to coatings developed in the 1970s to replace copper-based toxicants in marine antifouling coatings. The newest organotin-based marine antifouling coatings contain toxicants which are released from a polymer backbone upon exposure to water. The released toxicants adversely affect the larval forms of marine fouling organisms.
Tributyltin-based coatings have a much longer service life with concomitant savings in fuel and maintenance costs compared with copper-based compounds. Indeed, tributyltin compounds have been found to be very effective biocidal agents.
Unfortunately, the use of tributyltin compounds as antifoulants for ships' hulls is not environmentally as benign as federal and state environmental guidelines require. More particularly, tributyltin compounds persist in the water column and sediments and have the potential for bioaccumulation. In other words, tributyltin compounds tend to be environmentally hazardous as defined by current environmental statutes, because they do not quickly degrade, i.e., they do not quickly break down to less toxic derivatives after fulfilling their biocide function. It will be appreciated that the same environmental considerations apply to other applications, e.g., to bathroom paint applications, wherein water which contacts the paint can retain the toxic compounds and can ultimately be washed off the walls into sewage lines.
As recognized in previous U.S. Pat. No. 5,006,554 for an invention entitled "Organotin Compounds", it is possible to provide an organotin compound which is an effective biocidal agent, and which degrades much faster than tributyltin to a less-toxic species. In the above-mentioned U.S. patent, tributyltin is replaced by tributenyltin, and the tributenyltin has been found to be a very effective biocidal agent which quickly degrades to a less-toxic species. More particularly, tributenyltin is an effective biocide which degrades about an order of magnitude more quickly than tributyltin.
Unfortunately, it has been found that when tributenyltin compounds are esterified to copolymers for antifouling marine paint applications, the resulting polymers are intractable. Stated differently, the insolubility of tributenyltin-based polymers in common organic solvents severely hampers their use as marine antifouling coatings.